Generally, this kind of air intake device comprises an air cleaner incorporating a filter element, an atmospheric air introduction pipe for introducing atmospheric air into the air cleaner, and an intake pipe for introducing the air cleaned by the air cleaner into the intake manifold in the internal combustion engine. To enhance the air intake efficiency of the internal combustion engine, the atmospheric air introduction pipe and the intake pipe need to have a sufficient length.
The Patent Document 1 as a prior art proposes to arrange an air cleaner on a head cover covering the upper surface of a cylinder head in an internal combustion engine. The air cleaner includes two divided parts and a filter element sandwiched therebetween.
In the structure proposed by the Patent Document 2 as another prior art, a surge tank in an intake manifold is provided on a head cover covering the upper surface of a cylinder head of an internal combustion engine so that an end of the surge tank projects from a longitudinal end of the head cover. An air cleaner is arranged at a lower surface of the surge tank at a portion which projects from the head cover.
The Patent Document 3 as another prior art proposes to arrange a casing, which includes two vertically divided parts, on a head cover covering the upper surface of a cylinder head of an internal combustion engine. In the casing, an air cleaner and an atmospheric air introduction pipe for introducing air to the air cleaner are incorporated, and an intake pipe for guiding air from the air cleaner to the intake manifold is provided.
However, to arrange an air cleaner on the upper side of a head cover covering the upper surface of a cylinder head like the Patent Document 1 causes the following problems.
Since the entirety of the air cleaner projects from the upper surface of the head cover, the total height of the internal combustion engine considerably increases.
Further, since the atmospheric air introduction pipe needs to have a sufficient length to enhance the air intake efficiency, the atmospheric air introduction pipe projects largely from the internal combustion engine in plan view. Therefore, space for accommodating such a projecting portion needs to be secured around the internal combustion engine.
Moreover, the intake pipe extending from the air cleaner to the intake manifold cannot have a length sufficient to enhance the air intake efficiency.
In the structure disclosed in the Patent Document 2 again, the atmospheric air introduction pipe for introducing air to the air cleaner projects from the internal combustion engine. Therefore, space for accommodating the atmospheric air introduction pipe needs to be secured around the internal combustion engine. Further, an intake passage having a length sufficient to enhance the air intake efficiency cannot be defined between the air cleaner and the surge tank in the intake manifold.
With the structure disclosed in the Patent Document 3, the entirety of the air cleaner projects from the upper surface of the head cover, similarly to the structure of the Patent Document 1. Therefore, the total height of the internal combustion engine considerably increases.
Patent Document 1: JP-A 2002-97920
Patent Document 2: JP-A 2003-239815
Patent Document 3: JP-A 2003-161216